1. The Field of the Invention
The present invention relates to an optical photometry system for measuring pulsed light signals from optic probes used in the analysis of industrial fluid streams.
2. The Prior Art
There are a great many industrial processes which include fluid streams and which have need to monitor aspects of the flowing streams. These processes include those that are designed to modify the chemical composition of one or more sources to the streams. For example, chemical synthesis processes convert source streams of chemical reactants into chemical products. A process designed to remove oil or other contaminants from a source water stream is another example. Other types of processes use fluid streams to produce a desired physical environment. An example of this type of process would be a water cooling system designed to reduce the temperature of an internal combustion engine. Although there are many different types of fluid processes, they all are controlled in one way or another by the chemical composition of their fluid streams. Because of this, it is important to monitor the chemical composition of fluid streams in real-time, so that the information can be used to optimize the process's parameters before the process is complete.
There are also a great many processes involving bodies of liquid into which a treating agent is added. Maintaining the proper feed level of the agent can be critical to the optimal performance of many of these processes. For example, severe corrosion and/or deposit formation can occur rapidly on heat-exchange surfaces of cooling and boiling water systems if an incorrect level of treating agent is used. One common method of estimating concentration levels focuses on measuring the level of an active component of the treating agent, such as a polymeric scale inhibitor, phosphate or organophosphonate. This may not always be a suitable method due to background interferences and the bulky, labor intensive equipment which is currently available. A known method for determining the optimum feed rate of a treating agent is described in U.S. Pat. No. 4,783,314, the disclosure of which is incorporated herein by reference.
There are a great many analytical methods for determining the concentration of chemical substances in industrial fluid streams. Many methods are optical in nature; that is, they are based upon the inherent ability of a chemical substance to absorb, emit or reflect light in a manner proportional to its concentration. Chemical additives that do not possess inherent optical properties can nonetheless be determined indirectly by optical techniques if an optical tracer is added to the chemical prior to its addition to a fluid stream. A known method for such an indirect determination, based upon the addition of fluorescent dye to a chemical product, is also described in the above mentioned U.S. Pat. No. 4,783,314.
A variety of optical spectrometers are commercially available for the on-line analysis of industrial fluid streams. Examples of these are the Models 260 and 300 manufactured by Guided Wave, Inc. of El Dorado Hills, Calif. None of these known instruments, however, are designed for long term use in harsh industrial environments. Their light detection systems require continuous beams of light in order to operate. These beams are produced by a variety of continuous light sources which generate large amounts of heat. This results in rapid build-up of heat inside the instrument case and the requirement that such instruments be operated at ambient temperatures not greater than 35.degree. C. Many industrial process sites, especially those in the oil industry, have ambient temperatures in excess of 55.degree. C. Therefore, installation of these know instruments in such an environment would require additional facilities for climate control. In addition, the long-term utility of these known instruments is limited by the myriad of moving parts that are used for wavelength selection and optical multiplexing. The abrasive and corrosive conditions of some industrial environments (e.g. blowing sand and acid gases found in oil producing fields), often lead to the rapid failure of such mechanical devices.
The subject invention improves upon existing commercial optical on-line analysis instruments by providing a general purpose filter photometry system which can be configured for absorption, fluorescence and reflectance measurements in the ultraviolet, visible and near infrared spectral ranges. Conversion from one type of measurement to the other is achieved simply by selecting the appropriate light source, detector and optical probe. The instrument utilizes brief flashes of light which can be generated by a variety of pulsed light sources. Since pulsed light sources can generate extremely high light intensities, without generating correspondingly large amounts of heat, the present invention can be operated at the high ambient temperatures often encountered in industrial environments, while still allowing ultra-low detection limits, as low as parts per trillion for some fluorescent substances. Its pulsed mode of operation also allows light signals from several fiber optic probes to be sequentially monitored by a single photodetector. This is accomplished by flashing the excitation light source for each optical probe in sequence, so that only one signal reaches the detector at any given time. This temporal approach to optical multiplexing is rapid, extremely reproducible, and requires no moving parts. It is a significant improvement over spatial fiber optic multiplexers which are very slow, mechanically complex, and suffer from poor reproducibility. A dual-channel integrator simultaneously measures the light intensity emitted by the pulsed source and the resulting pulsed light intensity from an analytical probe. This allows each flash of the light source to yield an analytical signal that has been corrected for source fluctuations. Instrument performance is therefore not degraded as the pulsed light source becomes more erratic with age. The temporal multiplexing design also allows internal reference signals to be interspersed between analytical probe signals, making it possible to correct instrument response for drifting photodetector sensitivity.